U.S. patent application number 09/992135 was filed with the patent office on 2002-05-02 for method of eliminating agglomerate particles in a polishing slurry.
This patent application is currently assigned to Lucent Technologies Inc.. Invention is credited to Crevasse, Annette M., Easter, William G., Maze, John A., Merchant, Sailesh M., Miceli, Frank.
Application Number | 20020052115 09/992135 |
Document ID | / |
Family ID | 22175994 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020052115 |
Kind Code |
A1 |
Crevasse, Annette M. ; et
al. |
May 2, 2002 |
Method of eliminating agglomerate particles in a polishing
slurry
Abstract
The present invention, in one embodiment, provides a method for
eliminating agglomerate particles in a polishing slurry. In this
particular embodiment, the method is directed to reducing
agglomeration of slurry particles within a waste slurry passing
through a slurry system drain. The method comprises conveying the
waste slurry to the drain, wherein the waste slurry may form an
agglomerate having an agglomerate particle size. The method further
comprises subjecting the waste slurry to energy emanating from an
energy source. The energy source thereby transfers energy to the
waste slurry to substantially reduce the agglomerate particle size.
Substantially reduce means that the agglomerate is size is reduced
such that the waste slurry is free to flow through the drain.
Inventors: |
Crevasse, Annette M.;
(Apoka, FL) ; Easter, William G.; (Orlando,
FL) ; Maze, John A.; (Orlando, FL) ; Merchant,
Sailesh M.; (Orlando, FL) ; Miceli, Frank;
(Orlando, FL) |
Correspondence
Address: |
HITT GAINES & BOISBRUN P.C.
P.O. BOX 832570
RICHARDSON
TX
75083
US
|
Assignee: |
Lucent Technologies Inc.
600 Mountain Avenue
Murray Hill
NJ
07974-0636
|
Family ID: |
22175994 |
Appl. No.: |
09/992135 |
Filed: |
November 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09992135 |
Nov 14, 2001 |
|
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|
09427306 |
Oct 26, 1999 |
|
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09427306 |
Oct 26, 1999 |
|
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09083072 |
May 21, 1998 |
|
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Current U.S.
Class: |
438/691 ; 216/38;
257/E21.23 |
Current CPC
Class: |
B24B 37/04 20130101;
B24B 57/02 20130101; B24B 1/04 20130101 |
Class at
Publication: |
438/691 ;
216/38 |
International
Class: |
H01L 021/302; B44C
001/22 |
Claims
What is claimed is:
1. A method for reducing agglomeration of slurry particles in a
slurry system drain, comprising: conveying a waste slurry to the
drain, the waste slurry forming an agglomerate in the drain and
having an agglomerate particle size; subjecting the waste slurry to
energy emanating from an energy source; and transferring energy
from the energy source to the waste slurry to substantially reduce
the agglomerate particle size.
2. The method as recited in claim 1 further comprising sensing a
absorbance of the waste slurry with a absorbance sensor coupled to
the drain.
3. The method as recited in claim 2 wherein subjecting includes
cycling off the subjecting when the sensing discerns a nominal
absorbance or less, and cycling on the subjecting when the sensing
discerns greater than the nominal absorbance.
4. The method as recited in claim 3 wherein sensing a nominal
absorbance includes sensing a nominal absorbance of less than about
0.5.
5. The method as recited in claim 1 wherein transferring includes
transferring heat energy to the waste slurry.
6. The method as recited in claim 5 wherein transferring heat
energy includes transferring heat energy with a heating coil.
7. The method as recited in claim 5 wherein transferring heat
energy includes transferring heat energy with hot water.
8. The method as recited in claim 7 wherein transferring heat
energy with hot water includes transferring heat energy with hot
water by injection or by conduction.
9. The method as recited in claim 1 wherein transferring includes
transferring ultrasonic energy with an ultrasonic wave.
10. A system for reducing agglomerate particles of slurry in a
drain, comprising: a chemical/mechanical polishing apparatus; a
slurry source comprising a slurry and coupled to the
chemical/mechanical polishing apparatus; a slurry recovery system
having a drain configured to receive waste slurry from the
polishing apparatus, the waste slurry forming an agglomerate within
the drain and having an agglomerate particle size; and an energy
source proximate the drain and configured to transfer energy to the
waste slurry to substantially reduce the agglomerate particle
size.
11. The system as recited in claim 10 further comprising a
absorbance sensor coupled to the drain and configured to discern a
absorbance of the waste slurry.
12. The system as recited in claim 10 wherein the energy source is
a heat energy source.
13. The system as recited in claim 12 wherein the heat energy
source is a heating coil.
14. The system as recited in claim 12 wherein the heat energy
source is hot water.
15. The system as recited in claim 14 wherein the hot water is a
hot water injection device or a hot water jacket.
16. The system as recited in claim 10 wherein the energy source is
an ultrasonic transmitter.
17. A method of manufacturing an integrated circuit, comprising:
forming an active device on a semiconductor wafer; forming a
substrate over the active device; polishing the substrate with a
polishing tool using a polishing slurry thereby creating a waste
slurry; conveying the waste slurry to a drain, the waste slurry
forming an agglomerate in the drain and having an agglomerate
particle size; subjecting the waste slurry to energy emanating from
an energy source; and transferring energy from the energy source to
the waste slurry to substantially reduce the agglomerate particle
size.
18. The method as recited in claim 17 further comprising sensing a
absorbance of the waste slurry with a absorbance sensor coupled to
the drain.
19. The method as recited in claim 18 wherein the subjecting
includes cycling off the subjecting when the sensing discerns a
nominal absorbance or less, and cycling on the subjecting when the
sensing discerns greater than the nominal absorbance.
20. The method as recited in claim 19 wherein sensing a nominal
absorbance includes sensing a nominal absorbance of less than about
0.5.
21. The method as recited in claim 17 wherein transferring includes
transferring heat energy to the waste slurry with a heating coil or
with hot water.
22. The method as recited in claim 21 wherein transferring heat
energy with hot water includes transferring heat energy with hot
water by injection or by conduction.
23. The method as recited in claim 17 wherein transferring includes
transferring ultrasonic energy with an ultrasonic wave.
24. An integrated circuit as made by the method recited in claim
17.
25. The integrated circuit as recited in claim 24 wherein the
integrated circuit includes a transistor selected from the group
consisting of: a CMOS transistor, an NMOS transistor, a PMOS
transistor, and a bipolar transistor.
26. The integrated circuit as recited in claim 24 further
comprising electrical interconnects formed within the integrated
circuit.
27. The integrated circuit as recited in claim 26 wherein the
electrical interconnects include an electrical interconnect
selected from the group consisting of: a contact plug, a VIA, and a
trace.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation in part of U.S. patent
application Ser. No. 09/083,072, filed on May 21, 1998, entitled "A
Method of Eliminating Agglomerate Particles in a Polishing Slurry"
to Easter, et al., which is incorporated herein by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention is directed, in general, to a method
of semiconductor wafer fabrication and, more specifically to a
method of eliminating agglomerate particles in a polishing slurry
used for polishing a semiconductor wafer.
BACKGROUND OF THE INVENTION
[0003] Today's semiconductor technology is rapidly forcing device
sizes below the 0.5 micron level, even to the 0.25 micron size.
With device sizes on this order, even higher precision is being
demanded of the processes which form and shape the devices and the
dielectric layers separating the active devices. In the fabrication
of semiconductor components, the various devices are formed in
layers upon an underlying substrate typically composed of silicon,
germanium, or gallium arsenide. The various discrete devices are
interconnected by metal conductor lines to form the desired
integrated circuits. The metal conductor lines are further
insulated from the next interconnection level by thin films of
insulating material deposited by, for example, CVD (Chemical Vapor
Deposition) of oxide or application of SOG (Spin On Glass) layers
followed by fellow processes. Holes, or vias, formed through the
insulating layers provide electrical connectivity between
successive conductive interconnection layers. In such microcircuit
wiring processes, it is highly desirable that the insulating layers
have a smooth surface topography, since it is difficult to
lithographically image and pattern layers applied to rough
surfaces.
[0004] One semiconductor manufacturing process, chemical/mechanical
polishing (CMP), is used to provide the necessary smooth
semiconductor topographies. CMP can be used for planarizing: (a)
insulator surfaces, such as silicon oxide or silicon nitride,
deposited by chemical vapor deposition; (b) insulating layers, such
as glasses deposited by spin-on and reflow deposition means, over
semiconductor devices; or (c) metallic conductor interconnection
wiring layers such as tungsten. Semiconductor wafers may also be
planarized to: control layer thickness, define vias, remove a
hardmask, remove other material layers, etc. Significantly, a given
semiconductor wafer may be planarized several times, such as upon
completion of each metal layer. For example, following via
formation in a dielectric material layer, a metallization layer is
blanket deposited and then CMP is used to produce planar metal vias
or contacts.
[0005] Briefly, the CMP process involves holding and rotating a
thin, reasonably flat, semiconductor wafer against a rotating
polishing surface. The polishing surface is wetted by a chemical
slurry, under controlled chemical, pressure, and temperature
conditions. The chemical slurry contains a polishing agent, such as
alumina or silica, which is used as the abrasive material.
Additionally, the slurry contains selected chemicals which etch or
oxidize selected surfaces of the wafer to prepare them for removal
by the abrasive. The combination of both a chemical reaction and
mechanical removal of the material during polishing, results in
superior planarization of the polished surface. In this process it
is important to remove a sufficient amount of material to provide a
smooth surface, without removing an excessive amount of underlying
materials. Accurate material removal is particularly important in
today's submicron technologies where the layers between device and
metal levels are constantly getting thinner.
[0006] One problem area associated with chemical/mechanical
polishing is in the area of slurry consistency. The polishing
slurry is a suspension of a mechanical abrasive in a liquid
chemical agent. The mechanical abrasive, typically alumina or
amorphous silica, is chosen having a design particle size
specifically to abrade the intended material. The desired particle
size is chosen in much the same way that a sandpaper grade is
chosen to give a particular smoothness of finish on wood, metal, or
paint. If the particle size is too small, the polishing process
will proceed too slowly or not at all. However, if the particle
size is too large, desirable semiconductor features may be
significantly damaged by scratching or unpredictable removal rates.
Unfortunately, because the slurry is a suspension rather than a
solution, methods such as continual flow or high speed impellers
must be used to try to maintain a uniform suspension distribution.
The slurry particles tend to form relatively large clumps when
compared to semiconductor device sizes. While these clumps of
abrasive can grow to significant size, e.g., 0.1 .mu.m to 30 .mu.m,
depending in part upon their initial abrasive particle size, they
retain their ability to abrade the semiconductor wafer surface. The
agglomeration problem is most apparent when the slurry is allowed
to stand. If the slurry is allowed to stand in the supply line for
any appreciable time, the agglomeration begins and the slurry can
even gel, causing clogs in the supply line or unpredictable removal
rates. This results in the need to stop the processing and flush
the supply line. Of course, once the supply line is flushed, the
stabilized slurry must be reflowed through the line, forcing any
residual water from the line. This entire process is time consuming
and ultimately very expensive when the high cost of the wasted
slurry and the lost processing time is considered. Agglomeration is
especially a problem in metal planarization slurries.
[0007] To help alleviate this agglomeration problem, the
conventional approach has been to keep the slurry flowing in a loop
and to perform a coarse filter of the slurry while it is in the
loop. To supply the slurry to the polishing platen, the loop is
tapped, and the slurry is subjected to a point-of-use, final filter
just before it is applied to the polishing platen. However, as the
final filter strains out the larger particles, the filter becomes
clogged, raising the flow pressure required and necessitating a
filter change or cleaning operation. The increased pressure may
deprive the polishing platen of slurry and endanger the
planarization process. Cleaning or changing the filter clearly
interrupts the CMP processing. Naturally, cleaning or replacing the
filter is both time consuming and costly. Further, as the filters
are extremely fine (capable of passing particles less than about 10
.mu.m to 14 .mu.m in size), the filters themselves represent a
significant cost. Additionally, when the processing is stopped to
clean/replace the filter, the slurry supply line must be flushed
with water to prevent even more agglomerate from forming. This
flushing water initially dilutes the slurry when processing
resumes, further delaying the CMP process and affecting processing
parameters. Unfortunately, even when the filters are flushed
regularly, the filters may only last for a period of a few days or
even hours, depending upon the daily processing schedule.
Furthermore, these filters still allow particles that have particle
sizes larger than the intended design particle size to reach the
polishing surface.
[0008] Another problem area associated with chemical/mechanical
polishing is in the area of slurry agglomeration in the slurry
drain system. Unfortunately, the abrasive particles in the waste
slurry tend to agglomerate also in the drain, forming relatively
large clumps. This is a result of the slurry being gravity drained
to a waste slurry receptacle at room temperature whereas unused
slurry is held at a controlled temperature above room temperature
and pumped. The lower room temperature contributes to the waste
slurry agglomeration tendency, and the larger agglomerated
particles tend to collect in couplings, bends, and internally rough
areas of the drain. The agglomeration problem is very apparent if
the slurry is allowed to stand in the drain for any appreciable
time. When this happens, the drain line may clog. This may require
that the processing be stopped and the drain line be flushed. This
entire process is time consuming and ultimately very expensive in
lost processing time. Agglomeration is especially a problem in
metal planarization slurries.
[0009] To help alleviate this agglomeration problem in drains, the
conventional approach has been to use larger inside diameter drains
and to avoid or limit the number of sharp bends in the drain line.
Of course, this approach is limited by space constraints in the
clean room and does not directly address the problem.
[0010] Accordingly, what is needed in the art is a slurry transport
system and method of use thereof which efficiently breaks up the
CMP slurry agglomerate, and returns the slurry particulate matter
substantially to the design particle size.
SUMMARY OF THE INVENTION
[0011] To address the above-discussed deficiencies of the prior
art, the present invention, in one embodiment, provides a method
for eliminating agglomerate particles in a polishing slurry. In
this particular embodiment, the method is directed to reducing
agglomeration of slurry particles within a waste slurry passing
through a slurry system drain. The method comprises conveying the
waste slurry to the drain, wherein the waste slurry may form an
agglomerate having an agglomerate particle size. The method further
comprises subjecting the waste slurry to energy emanating from an
energy source. The energy source thereby transfers energy to the
waste slurry to substantially reduce the agglomerate particle size.
Substantially reduce means that the agglomerate is size is reduced
such that the waste slurry is free to flow through the drain.
[0012] In a particularly advantageous embodiment, the method
further comprises sensing a absorbance of the waste slurry with a
absorbance sensor coupled to the drain. The method, in another
embodiment, includes cycling off the energy source when the
absorbance sensed is a nominal absorbance or less. The method
further includes cycling the energy source on when the absorbance
sensed is greater than the nominal absorbance. In a further aspect,
the nominal absorbance may be less than about 0.5.
[0013] In one embodiment, the energy transferred to the waste
slurry is heat energy. In one specific aspect of this embodiment,
the heat energy is transferred with a heating coil. In an
alternative embodiment, the heat energy is transferred with hot
water. Transferring heat energy with hot water may include
injecting hot water or through conduction. In another embodiment,
the energy may be transferred as ultrasonic energy by an ultrasonic
wave.
[0014] The foregoing has outlined, rather broadly, preferred and
alternative features of the present invention so that those who are
skilled in the art may better understand the detailed description
of the invention that follows. Additional features of the invention
will be described hereinafter that form the subject of the claims
of the invention. Those who are skilled in the art should
appreciate that they can readily use the disclosed conception and
specific embodiment as a basis for designing or modifying other
structures for carrying out the same purposes of the present
invention. Those who are skilled in the art should also realize
that such equivalent constructions do not depart from the spirit
and scope of the invention in its broadest form.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a more complete understanding of the present invention,
reference is now made to the following descriptions taken in
conjunction with the accompanying drawings, in which:
[0016] FIGS. 1A and 1B illustrate schematic sectional and plan
views of an exemplary embodiment of a conventional
chemical/mechanical planarization (CMP) apparatus for use in
accordance with the method of the current invention;
[0017] FIG. 2 illustrates a table of representative, commercially
available slurries from one manufacturer for use with the present
invention;
[0018] FIG. 3 illustrates a schematic view of one embodiment of an
improved CMP slurry delivery system constructed according to the
principles of the present invention;
[0019] FIG. 4 illustrates a schematic sectional view of an
exemplary embodiment of a conventional chemical/mechanical
planarization (CMP) apparatus for use in accordance with the method
of the present invention;
[0020] FIG. 5 illustrates the conventional CMP apparatus of FIG. 4
with one embodiment of a waste slurry recovery system constructed
according to the principles of the present invention;
[0021] FIG. 6A illustrates the conventional CMP apparatus of FIG. 4
with an alternative embodiment of a waste slurry recovery
system;
[0022] FIG. 6B illustrates the conventional CMP apparatus of FIG. 4
with an alternative embodiment of the waste slurry recovery system
of FIG. 6A;
[0023] FIG. 7 illustrates the conventional CMP apparatus of FIG. 4
with a second alternative embodiment of the waste slurry recovery
system of the present invention; and
[0024] FIG. 8 illustrates a partial sectional view of a
conventional integrated circuit that can be manufactured using the
slurry recovery system constructed in accordance with the
principles of the present invention.
DETAILED DESCRIPTION
[0025] To address the deficiencies of the prior art, the present
invention provides a unique chemical/mechanical planarization (CMP)
slurry delivery system that can eliminate agglomeration that occur
in a slurry used in polishing or planarizing a semiconductor wafer.
The general method of planarizing the surface of a semiconductor
wafer, using CMP polishing, and the new and improved slurry
delivery system will now be described in detail. The method may be
applied when planarizing: (a) insulator surfaces, such as silicon
oxide or silicon nitride, deposited by chemical vapor deposition;
(b) insulating layers, such as glasses deposited by spin-on and
reflow deposition means, over semiconductor devices; or (c)
metallic conductor interconnection wiring layers.
[0026] Referring initially to FIG. 1A, illustrated is a schematic
sectional view of an exemplary embodiment of a conventional
chemical/mechanical planarization (CMP) apparatus for use in
accordance with the method of the invention. The CMP apparatus 100
may be of a conventional design that includes a wafer carrier or
polishing head 110 for holding a semiconductor wafer 120. The wafer
carrier 110 typically comprises a retaining ring 115, which is
designed to retain the semiconductor wafer 120. The wafer carrier
110 is mounted to a drive motor 130 for continuous rotation about
axis A.sub.1 in a direction indicated by arrow 133. The wafer
carrier 110 is adapted so that a force indicated by arrow 135 is
exerted on the semiconductor wafer 120. The CMP apparatus 100
further comprises a polishing platen 140 mounted to a second drive
motor 141 for continuous rotation about axis A.sub.2 in a direction
indicated by arrow 143. A polishing pad 145 formed of a material,
such as blown polyurethane, is mounted to the polishing platen 140,
which provides a polishing surface for the process. During CMP, a
polishing slurry 150, which comprises an abrasive material in a
colloidal suspension of either a chemical solution, is dispensed
onto the polishing pad 145. In a particularly advantageous
embodiment, the abrasive material may be amorphous silica or
alumina and has a design, i.e., specification, particle size chosen
for the material being polished. During CMP, the polishing slurry
150 is continuously pumped by a main slurry pump 160 from a slurry
source tank 170, through a primary filter 161, around a main slurry
loop 163, then back to the slurry source tank 170. A portion of the
polishing slurry 150 circulating in the main slurry loop 163 is
diverted through a three-way solenoid valve 165 to a slurry
delivery conduit 167 and pumped to a dispensing mechanism 180,
through a final filter 181, and onto the polishing pad 145 by a
slurry delivery pump 190. This final filter 181 is only effective
in removing agglomerated particles greater than 10 .mu.m in size.
With linewidths at 0.25 .mu.m and less, these agglomerated
particles can severely damage the interconnect circuits. A water
source is coupled to the solenoid valve 165 for flushing the slurry
delivery conduit 167, the dispensing mechanism 180, and the slurry
delivery pump 190.
[0027] Referring now to FIG. 1B, illustrated is a schematic plan
overhead view of the CMP apparatus of FIG. 1A with the key elements
shown. The wafer carrier 110 is shown to rotate in a direction
indicated by arrow 133 about the axis A.sub.1. The polishing platen
140 is shown to rotate in a direction indicated by arrow 143 about
the axis A.sub.2. Controlled by the three-way solenoid valve 165,
the polishing slurry 150 is dispensed onto the polishing pad 145,
through the delivery conduit 167 and the dispensing mechanism 180,
from the slurry source tank 170. Those who are skilled in the art
are familiar with the operation of a conventional CMP
apparatus.
[0028] Referring now to FIG. 2 with continuing reference to FIGS.
1A and 1B, illustrated is a table of representative, commercially
available slurries from one manufacturer for use with the present
invention. Commercially available slurries, generally designated
200, with Solution Technology Incorporated product designations
(Column 210) shown, comprise abrasive particles of alumina or
amorphous silica (Column 220) held in colloidal suspension in
selected chemicals (Column 230) at the concentrations (Column 240)
and design pH (Column 250) shown. The selected chemicals 230
oxidize or react with a selected material (Column 270) on the
semiconductor wafer 120. The oxidized or reacted portion is then
removed by a mechanical abrasive process. As can be seen in Column
260, the slurry particles of alumina or amorphous silica 220 have
design, i.e., specification, particle sizes ranging from about
0.012 microns to about 1.5 microns.
[0029] Referring now to FIG. 3, illustrated is a schematic view of
one embodiment of an improved CMP slurry delivery system
constructed according to the principles of the present invention.
An improved CMP slurry delivery system, generally designated 300,
comprises the essential elements of the conventional slurry
delivery system of FIGS. 1A and 1B, i.e., the slurry source tank
170, the main slurry pump 160, the primary filter 161, the main
slurry loop 163, the three-way solenoid valve 165, the slurry
delivery conduit 167, the slurry dispensing mechanism 180, and the
slurry delivery pump 190.
[0030] The improved CMP slurry delivery system 300 may further
comprise an energy source 310. In one advantageous embodiment, the
energy source 310 comprises a 24 volt power source 311, a power
control solenoid 313, a radio frequency generator 315, an RF coax
cable 317, and an ultrasonic dispenser nozzle 319. In this
embodiment, the 24 volt power source 311 is electrically coupled to
the radio frequency generator 315 and the slurry delivery pump 190
through the power control solenoid 313. Thus, the power control
solenoid 313 controls electrical power to both the radio frequency
generator 315 and the slurry delivery pump 190. The radio frequency
generator 313 is further coupled to the ultrasonic dispenser nozzle
319 by the wave guide 317. The ultrasonic dispenser nozzle 319 is
mechanically coupled to the output nozzle 380 of the slurry
dispensing mechanism 180. In one advantageous embodiment, the radio
frequency generator 313 may be capable of emitting ultrasonic
energy from about 1 mega Hertz (MHZ) to about 15 MHZ and at a power
of about 20 watts. In this embodiment, the ultrasonic energy
transmitted to the ultrasonic dispenser nozzle 319 by the wave
guide 317 is focused on the slurry 200 that is flowing through the
ultrasonic dispenser nozzle 319.
[0031] With the equipment of the improved CMP slurry delivery
system 300 having been described, its operation will now be
discussed in an embodiment in relation to CMP of a semiconductor
wafer 120 to planarize a tungsten plug layer. Referring now
simultaneously to FIGS. 1A, 1B, and 3, the CMP apparatus is
prepared for processing the semiconductor wafer 120. All components
of the improved slurry delivery system 300 have been thoroughly
cleaned from prior processes. The slurry source tank 170 is filled
with an appropriate slurry 200 (e.g., MET-200) from FIG. 2 and the
main slurry pump 160 is activated. In this particular embodiment,
the semiconductor surface being planarized is a metal, i.e.,
tungsten, and the alumina abrasive particle size is about 1.5
.mu.m. In alternative embodiments for planarizing metals, e.g.,
aluminum, copper, or tungsten, the alumina abrasive particle size
may vary from about 0.12 .mu.m to about 1.5 .mu.m. In yet other
alternative embodiments, the planarizing of a dielectric material,
i.e., semiconductor oxides, may employ amorphous silica with
particle sizes ranging from about 0.012 .mu.m to about 0.05 .mu.m.
A person who is skilled in the art will readily appreciate that
other abrasives and other particle sizes may likewise be employed
with the present invention.
[0032] The slurry 200 flows through the primary slurry filter 161
and around the main slurry loop 163, then back to the slurry source
tank 170. This flow will continue throughout the CMP processing.
Regardless of this flow, however, experience has shown that
particle agglomeration occurs. Those particles larger than the
actual interstitial spacing of the primary slurry filter 161 will
be captured by the filter 161. Agglomerated particles of sizes from
about 0.1 .mu.m to about 30 .mu.m may escape capture by the filter
161, however, and be diverted to the slurry delivery conduit 167 by
three-way solenoid valve 165 along with slurry particles of the
design size. Moreover, experience has also shown that agglomerated
particles form in the slurry delivery conduits even after passing
through the filter 161.
[0033] Before CMP begins, the power control solenoid 313 is
energized and applies electrical power to the slurry delivery pump
190 and the radio frequency generator 315. Agglomerated slurry
particles not captured by the primary slurry filter 161 may be in
the slurry 200 diverted to the slurry delivery conduit 167 and
pumped through the slurry dispensing mechanism 180 by the slurry
delivery pump 190.
[0034] The energized radio frequency generator 315 delivers radio
frequency energy in the form of an ultrasonic wave to the
ultrasonic dispenser nozzle 319 through the wave guide 317. The
ultrasonic wave is of a frequency from about 1 MHZ to about 15 MHZ
and at a power of about 20 watts. When the slurry 200 passes
through the ultrasonic dispenser nozzle 319, the ultrasonic wave
transmitted from the radio frequency generator 313 is focused by
the nozzle 319 on the slurry 200. The ultrasonic energy transferred
to the slurry 200 is absorbed by the agglomerated particles. One
who is skilled in the art is familiar with the mechanism by which
energy in the form of an ultrasonic wave is used to break up
particulate material. In a preferred embodiment, the frequency of
the ultrasonic energy applied to the slurry 200 is selectively
controlled at a frequency between about 1 MHZ and about 15 MHZ,
with a power of about 20 watts, so as to reduce the agglomerated
particle size to substantially the design particle size for the
slurry product 200 in use. The output power and frequency of the
radio frequency generator 315 is carefully controlled so that the
agglomerated particles are not reduced in size below the design
particle size.
[0035] Referring now to FIG. 4, illustrated is a schematic
sectional view of an exemplary embodiment of a conventional
chemical/mechanical planarization (CMP) apparatus for use in
accordance with the method of the present invention. The CMP
apparatus 400 may be of a conventional design that includes a wafer
polishing platen 410 and carrier head 415 for polishing a
semiconductor wafer 420 in a slurry catch basin 430. The CMP
apparatus 400 further comprises a slurry source 440, a fresh slurry
delivery system 441, and a waste slurry recovery system 450.
[0036] During CMP, slurry 455 is delivered to the polishing platen
410 by the fresh slurry delivery system 440. After polishing the
semiconductor wafer 420, the waste slurry 457 collects in the
slurry catch basin 430. From the slurry catch basin 430, the waste
slurry 457 is routed to a drain 435 to be collected in a waste
slurry recovery tank 437. In the drain 435, the waste slurry 457 is
conventionally allowed to drain by gravity at room temperature.
Because the waste slurry 457 is cooling and not being pumped under
pressure, any bend 438 in the drain 435 may be a potential catalyst
for the waste slurry 457 to agglomerate to a sizeable particle
size. Ultimately, the agglomerated particles may block the drain
435.
[0037] Referring now to FIG. 5, illustrated is the conventional CMP
apparatus of FIG. 4 with one embodiment of a waste slurry recovery
system 500 constructed according to the principles of the present
invention. The waste slurry recovery system 500 comprises a
absorbance sensor 510 and an energy source 520. In the illustrated
embodiment, the energy source 520 is coupled to a heating coil 525
wrapped about the drain 435. The absorbance sensor 510 is coupled
to the drain 435 and senses a absorbance of the waste slurry 457.
If the absorbance sensed is equal to or greater than a nominal
absorbance, the absorbance sensor 510 is programmed to turn the
heating coil 525 on. The nominal absorbance is predetermined from
empirical data to be the value at which agglomeration becomes a
problem that may cause blockage of the drain 435. The nominal
absorbance will vary with the type and composition of the slurry.
By cycling the heating coil 525 on, the waste slurry 457 is
subjected to heat energy that contributes to a higher energy state
of the waste slurry 457. With increased temperature, the waste
slurry 457 is less likely to agglomerate to the point at which
drain 435 blockage occurs, that is, the agglomerated particle size
is substantially reduced by the addition of heat energy to the
waste slurry. The term "substantially reduced" means that the
agglomerated particle size is reduced to a degree that the waste
slurry 457 flows freely through the drain 435 to the waste slurry
recovery tank 437. If the absorbance sensor 510 determines that the
waste slurry absorbance is less than the nominal absorbance, the
absorbance sensor 510 cycles the heating coil 525 off, as energy is
not needed to prevent blockage.
[0038] While the present discussion relates to a absorbance sensor,
one who is skilled in the art will readily conceive of other
sensors that can perform a similar task, i.e., flow meters,
viscosimeters, etc. Such other sensors are considered to be within
the greater scope of the present invention.
[0039] Referring now to FIG. 6A, illustrated is the conventional
CMP apparatus of FIG. 4 with an alternative embodiment of a waste
slurry recovery system 600. In this embodiment, the waste slurry
recovery system 600 comprises a absorbance sensor 610 and an energy
source 620. In the illustrated embodiment, the energy source 620 is
a hot water source 625 coupled to the drain 435. Coupling of the
hot water source 625 to the drain 435 is by forming a water jacket
627 about the drain 435. If the absorbance sensed is equal to or
greater than the nominal absorbance, the absorbance sensor 610 is
programmed to circulate hot water through the water jacket 627.
This transfers heat energy to the waste slurry 457 by conduction
and reduces the probability of slurry particle agglomeration in
much the same way as the embodiment of FIG. 5. This embodiment
further comprises a recirculation circuit 628 including a
recirculation pump 629. By recirculating the hot water, the water
and the energy left in the water is not wasted, but rather is
efficiently recycled.
[0040] Referring now to FIG. 6B, illustrated is the conventional
CMP apparatus of FIG. 4 with an alternative embodiment of the waste
slurry recovery system of FIG. 6A. In this embodiment, the waste
slurry recovery system 650 comprises a absorbance sensor 610 and an
energy source 620. The energy source 620 is a hot water source 625
coupled to the drain 435. The hot water source 625 is coupled to
the drain 435 by a hot water line 627. When the absorbance sensed
is equal to or greater than the nominal absorbance, the absorbance
sensor 610 injects hot water into the drain 435. Heat from the hot
water adds energy to the waste slurry 457, thereby increasing the
energy state of the waste slurry 457 and reducing the probability
of agglomeration of the slurry particles. In addition, the flowing
water helps to add kinetic energy to the waste slurry 457, further
reducing the probability of agglomeration. Of course, the point of
injection may be varied along the drain 435.
[0041] Referring now to FIG. 7, illustrated is the conventional CMP
apparatus of FIG. 4 with a second alternative embodiment of the
waste slurry recovery system of the present invention. In this
particularly advantageous embodiment, the waste slurry recovery
system 700 comprises a absorbance sensor 710 and an energy source
720. The energy source 720 comprises an electrical power source 720
coupled to an ultrasonic transducer 725. When required by the
absorbance sensor 710, electrical power is applied by the energy
source 720 to the ultrasonic transducer 725 and ultrasonic waves
727. are applied to the waste slurry 457, increasing the energy
state of the waste slurry 457 and reducing the probability of
agglomeration.
[0042] Referring now to FIG. 8, illustrated is a partial sectional
view of a conventional integrated circuit 800 that can be
manufactured using the slurry recovery system constructed in
accordance with the principles of the present invention. In this
particular sectional view, there is illustrated an active device
810 that comprises a tub region 820, source/drain regions 830 and
field oxides 840, which together may form a conventional
transistor, such as a CMOS, PMOS, NMOS or bi-polar transistor. A
contact plug 850 contacts the active device 810. The contact plug
850 is, in turn, contacted by a trace 860 that connects to other
regions of the integrated circuit, which are not shown. A VIA 870
contacts the trace 860, which provides electrical connection to
subsequent levels of the integrated circuit. One who is skilled in
the art is familiar with the need to planarize the integrated
circuit 800 several times during manufacture. Such planarization
may necessitate removal and maintenance of the polishing head with
the described invention.
[0043] From the foregoing, it is apparent that the present
invention provides a method and system for eliminating agglomerate
particles in a polishing slurry. The method includes transferring a
slurry that has a design particle size from a slurry source to an
energy source. In many instances, the slurry forms an agglomerate
that can accumulate in the waste slurry drain and cause a blockage.
The method further includes subjecting the agglomerate to energy,
such as: heat, hot water, or an ultra sonic wave, emanating from
the energy source and transferring energy from the energy source to
the slurry to reduce the agglomerated particle size to reduce the
probability of drain blockage.
[0044] Although the present invention has been described in detail,
those who are skilled in the art should understand that they can
make various changes, substitutions and alterations herein without
departing from the spirit and scope of the invention in its
broadest form.
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